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virt: sevguest: Fix passing a stack buffer as a scatterlist target

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CONFIG_DEBUG_SG highlights that get_{report,ext_report,derived_key)()}
are passing stack buffers as the @req_buf argument to
handle_guest_request(), generating a Call Trace of the following form:

    WARNING: CPU: 0 PID: 1175 at include/linux/scatterlist.h:187 enc_dec_message+0x518/0x5b0 [sev_guest]
    [..]
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
    RIP: 0010:enc_dec_message+0x518/0x5b0 [sev_guest]
    Call Trace:
     <TASK>
    [..]
     handle_guest_request+0x135/0x520 [sev_guest]
     get_ext_report+0x1ec/0x3e0 [sev_guest]
     snp_guest_ioctl+0x157/0x200 [sev_guest]

Note that the above Call Trace was with the DEBUG_SG BUG_ON()s converted
to WARN_ON()s.

This is benign as long as there are no hardware crypto accelerators
loaded for the aead cipher, and no subsequent dma_map_sg() is performed
on the scatterlist. However, sev-guest can not assume the presence of
an aead accelerator nor can it assume that CONFIG_DEBUG_SG is disabled.

Resolve this bug by allocating virt_addr_valid() memory, similar to the
other buffers am @snp_dev instance carries, to marshal requests from
user buffers to kernel buffers.

Reported-by: Peter Gonda <pgonda@google.com>
Closes: http://lore.kernel.org/r/CAMkAt6r2VPPMZ__SQfJse8qWsUyYW3AgYbOUVM0S_Vtk=KvkxQ@mail.gmail.com
Fixes: fce96cf044 ("virt: Add SEV-SNP guest driver")
Cc: Borislav Petkov <bp@alien8.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Dionna Glaze <dionnaglaze@google.com>
Cc: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Tested-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams 2023-10-10 12:53:33 -07:00
parent 6465e260f4
commit db10cb9b57
1 changed files with 25 additions and 20 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

45
drivers/virt/coco/sev-guest/sev-guest.c
View file

@ -57,6 +57,11 @@ struct snp_guest_dev {
struct snp_secrets_page_layout *layout;
struct snp_req_data input;
union {
struct snp_report_req report;
struct snp_derived_key_req derived_key;
struct snp_ext_report_req ext_report;
} req;
u32 *os_area_msg_seqno;
u8 *vmpck;
};
@ -473,8 +478,8 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
{
struct snp_guest_crypto *crypto = snp_dev->crypto;
struct snp_report_req *req = &snp_dev->req.report;
struct snp_report_resp *resp;
struct snp_report_req req;
int rc, resp_len;
lockdep_assert_held(&snp_cmd_mutex);
@ -482,7 +487,7 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
if (!arg->req_data || !arg->resp_data)
return -EINVAL;
if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
if (copy_from_user(req, (void __user *)arg->req_data, sizeof(*req)))
return -EFAULT;
/*
@ -496,7 +501,7 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
return -ENOMEM;
rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
SNP_MSG_REPORT_REQ, &req, sizeof(req), resp->data,
SNP_MSG_REPORT_REQ, req, sizeof(*req), resp->data,
resp_len);
if (rc)
goto e_free;
@ -511,9 +516,9 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
{
struct snp_derived_key_req *req = &snp_dev->req.derived_key;
struct snp_guest_crypto *crypto = snp_dev->crypto;
struct snp_derived_key_resp resp = {0};
struct snp_derived_key_req req;
int rc, resp_len;
/* Response data is 64 bytes and max authsize for GCM is 16 bytes. */
u8 buf[64 + 16];
@ -532,11 +537,11 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
if (sizeof(buf) < resp_len)
return -ENOMEM;
if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
if (copy_from_user(req, (void __user *)arg->req_data, sizeof(*req)))
return -EFAULT;
rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
SNP_MSG_KEY_REQ, &req, sizeof(req), buf, resp_len);
SNP_MSG_KEY_REQ, req, sizeof(*req), buf, resp_len);
if (rc)
return rc;
@ -552,8 +557,8 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
{
struct snp_ext_report_req *req = &snp_dev->req.ext_report;
struct snp_guest_crypto *crypto = snp_dev->crypto;
struct snp_ext_report_req req;
struct snp_report_resp *resp;
int ret, npages = 0, resp_len;
@ -562,18 +567,18 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
if (!arg->req_data || !arg->resp_data)
return -EINVAL;
if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
if (copy_from_user(req, (void __user *)arg->req_data, sizeof(*req)))
return -EFAULT;
/* userspace does not want certificate data */
if (!req.certs_len || !req.certs_address)
if (!req->certs_len || !req->certs_address)
goto cmd;
if (req.certs_len > SEV_FW_BLOB_MAX_SIZE ||
!IS_ALIGNED(req.certs_len, PAGE_SIZE))
if (req->certs_len > SEV_FW_BLOB_MAX_SIZE ||
!IS_ALIGNED(req->certs_len, PAGE_SIZE))
return -EINVAL;
if (!access_ok((const void __user *)req.certs_address, req.certs_len))
if (!access_ok((const void __user *)req->certs_address, req->certs_len))
return -EFAULT;
/*
@ -582,8 +587,8 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
* the host. If host does not supply any certs in it, then copy
* zeros to indicate that certificate data was not provided.
*/
memset(snp_dev->certs_data, 0, req.certs_len);
npages = req.certs_len >> PAGE_SHIFT;
memset(snp_dev->certs_data, 0, req->certs_len);
npages = req->certs_len >> PAGE_SHIFT;
cmd:
/*
* The intermediate response buffer is used while decrypting the
@ -597,14 +602,14 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
snp_dev->input.data_npages = npages;
ret = handle_guest_request(snp_dev, SVM_VMGEXIT_EXT_GUEST_REQUEST, arg,
SNP_MSG_REPORT_REQ, &req.data,
sizeof(req.data), resp->data, resp_len);
SNP_MSG_REPORT_REQ, &req->data,
sizeof(req->data), resp->data, resp_len);
/* If certs length is invalid then copy the returned length */
if (arg->vmm_error == SNP_GUEST_VMM_ERR_INVALID_LEN) {
req.certs_len = snp_dev->input.data_npages << PAGE_SHIFT;
req->certs_len = snp_dev->input.data_npages << PAGE_SHIFT;
if (copy_to_user((void __user *)arg->req_data, &req, sizeof(req)))
if (copy_to_user((void __user *)arg->req_data, req, sizeof(*req)))
ret = -EFAULT;
}
@ -612,8 +617,8 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
goto e_free;
if (npages &&
copy_to_user((void __user *)req.certs_address, snp_dev->certs_data,
req.certs_len)) {
copy_to_user((void __user *)req->certs_address, snp_dev->certs_data,
req->certs_len)) {
ret = -EFAULT;
goto e_free;
}